Six American troops have been killed in a suicide attack near Bagram airfield in Afghanistan, US officials said.

Two others were wounded along with an Afghan when an attacker rammed an explosives-laden motorcycle into their patrol in a village near the airfield. The Taliban has claimed responsibility.

The attack comes days after US defence secretary Ash Carter stopped in Bagram. A recent Pentagon report said violence in Afghanistan has increased.

US Army Brigadier General William Shoffner, head of public affairs at Nato's Resolute Support base in the Afghan capital Kabul, said: "Our heartfelt sympathies go out to the families and friends of those affected in this tragic incident, especially during this holiday season."

It was the deadliest attack on foreign troops in four months. On August 22, three American contractors with the RS base were killed in a suicide attack in Kabul.

On August 7 and 8, Kabul was the scene of three insurgent attacks within 24 hours that left at least 35 people dead. One of the attacks, on a US special forces base outside Kabul, killed one US soldier and eight Afghan civilian contractors.